In the radiation medical field for the purpose of cancer therapy, there have been advanced, development of a particle beam therapy apparatus that is a cancer therapy apparatus using proton or a heavy ion, and construction of a facility in which the therapy is performed using the particle beam therapy apparatus. According to the therapy by a particle beam using proton, a heavy ion, etc., a cancer diseased site can be irradiated in a concentrated manner as compared to the conventional radiation therapy using an X-ray, a γ-ray, etc., and thus it is possible to perform the therapy without influencing normal cells.
In recent years, with respect to the particle beam therapy apparatuses, high-level three-dimensional irradiation methods that can reduce influence on normal cells, such as a scanning irradiation method and a layer-stacking conformal irradiation method, are developed and put into practical use. According to the high-level three-dimensional irradiation methods, the beam condition is finely changed during irradiation to thereby execute a more precious control of dose distribution than otherwise.
The particle beam therapy apparatus is configured with treatment rooms each having an irradiation device for irradiating a patient with a specified particle beam according to a treatment plan, and an accelerator for generating the particle beam and transporting the beam under a specified beam condition to the designated treatment room, in response to a particle-beam request from the treatment room.
Furthermore, the irradiation device includes a dose monitoring system that performs monitoring for controlling so that the patient is irradiated with the particle beam by a prescribed dose amount. Since the irradiation dose is one of the particularly important treatment parameters, the dose monitor in the dose monitoring system of the particle beam therapy apparatus is generally made redundant, to thereby enhance the reliability thereof.
For the conventional particle beam therapy apparatuses, such a technique is known in which a dose monitor for measuring the irradiation dose is duplicated by providing a main dose monitor and a sub dose monitor in beam line devices through which a proton beam passes (for example, Non-Patent Document 1).